The objectives of this project are to characterize the antigens of the rickettsiae and other bacteria which are pathogenic for humans. Structure and functional aspects of the immunomodulation by the cell wall and soluble components are currently being analyzed as potential candidates for subunit vaccines and as tumor-regressive components. Studies employing Coxiella burnetii have revealed a particulate component which is nontoxic, provides protection against a lethal challenge in mice and guinea pigs and regresses the line-10 tumors in strain-2 guinea pigs. This particulate material is potentially a nontoxic vaccine. Soluble components have been identified as putative early diagnostic antigens which induce specific antibody during infection but not after immunization.